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Taxonomy

Earthworms (Figure 1) are scientifically classified as
animals belonging to the order Oligochaeta, class Chaetopoda, phylum Annelida.
In this phylum there are about 1,800 species of earthworms grouped into five
families and distributed all over the world. The most common worms in North
America, Europe, and Western Asia belong to
the family Lumbricidae, which has about 220 species. Earthworms range from a
few millimeters long to over 3 feet, but most common species are a few inches
in length. Only a few types are of interest to the commercial earthworm grower,
and of these only two are raised on a large-scale commercial basis. Some of the
more common species used for bait are the following.

Figure 1. Earthworm.

Nightcrawlers. This
earthworm is common to the northern states and may be picked from fields
and lawns at night for commercial fish-bait sale. Although very popular
with fishermen, they are not commonly raised on a commercial basis because
they reproduce slowly and require special production and control
procedures.

Field worms (also
known as garden worms). These make excellent fish bait and are often
preferred by those who want a small number of worms for their own use.
They are not prolific breeders, so are not recommended for commercial
enterprises.

Manure worms (also
known as bandlings, red wigglers, or angleworms because of their squirming
reactions when handled). These are particularly adaptable to commercial
production and are one of the two types most commonly grown by successful
worm farmers.

Red worms. These are
basically another type of manure worm, differing mainly in size and color
from their larger and darker cousins. They are also very adaptable to
commercial production, and together with manure worms constitute about 80
to 90 percent of commercially-produced worms.

Manure worms and red worms can adapt to living in many
different environments. They will eat almost any organic matter at some stage
of decomposition, as well as many other types of materials which contain
organic substances that can be ingested.

These worms may be found in manure piles or in soils containing large
quantities of organic matter, but the new grower should purchase breeding stock
from a reputable grower or distributor. Breeder worms may be purchased in lots
as small as 1,000 worms. (One 8-foot by 3-foot by 1-foot deep bin, however, may
contain 100,000 worms or more.)

Biology

Because the physical structure of earthworms varies only
slightly from one species to another, a description of one species will apply
in most respects to any other. In this section, the nightcrawler, Lumbricus
terrestris, is used for descriptive purposes.

The earthworm, while primitive, has well-developed nervous, circulatory,
digestive, excretory, muscular, and reproductive systems, the major elements of
which are shown in Figure 2. The most
noticeable external feature (Figure 3) is the ringing or segmentation of the
body, which is not merely external but involves nearly all of the internal
structure. The nightcrawler has about 150 segments, while manure and red worms
have approximately 95. Segmentation within the earthworm serves the same
general function as the division of the animal body into organs--that is,
different segments perform different functions.

The first section of the earthworm, the anterior end or head, consists of
the mouth and the prostomium, a lobe which serves as a covering for the mouth
and as a wedge to force open cracks in the soil into which the earthworm may
crawl. Small hair-like structures, called setae (bristles), are located on each
segment. These can be extended or retracted and a principal function is for
movement. The worm's lack of protruding structures other than setae facilitates
efficient burrowing; in addition, various skin glands secrete a lubricating mucus
which aids movement through the earth and helps to stabilize burrows and casts.

The earthworm's digestive tract is highly adapted to its burrowing and
feeding activities. The worm swallows soil (including decomposing organic
residues in the soil) or residues and plant litter on the soil surface. Strong
muscles mix the swallowed material and pass it through the digestive tract as
digestive fluids containing enzymes are secreted and mixed with the materials.
The digestive fluids release amino acids, sugars, and other smaller organic
molecules from the organic residues (which include living protozoa, nematodes,
bacteria, fungi, and other microorganiams as well as partially decomposed plant
and animal materials). The simpler molecules are absorbed through intestinal
membranes and are utilized for energy and cell synthesis.

Reproduction. Earthworms are usually not self-mating although they
are hermaphroditic (each individual possesses both male and female reproductive
organs). A mutual exchange of sperm occurs between two worms during mating.
Mature sperm and egg cells and nutritive fluid are deposited in cocoons
produced by the clitellum, a conspicuous, girdle-like structure near the
anterior end of the body. The ova (eggs) are fertilized by the sperm cells
within the cocoon, which then slips off the worm and is deposited in or on the
soil. The eggs hatch after about 3 weeks, each cocoon producing from two to twenty
baby worms with an average of four.

Footnotes

1. This document is Circular 455, Florida Cooperative
Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
It was originally published as Leaflet 2828 for the Division of Agricultural
Sciences at the University
of California, July 1976,
and was reprinted as FCES Circular 455 in May 1979. Revised: June 2005.

2. The authors of Leaflet 2828 are J. P. Martin,
professor of Soil Science, Riverside, CA; J. H. Black, Farm Advisor (Entomology), Kern County,
Bakersfield, CA;
and R. M. Hawthorne, survey entomologist, Division of Plant Industry, State
Department of Food and Agriculture, Sacramento,
CA. This publication was reviewed
for use in Florida by R. A. Dunn, professor,
Department of Entomology and Nematology, Cooperative Extension Service, Institute of Food
and Agricultural Sciences, University
of Florida, Gainesville, 32611. This publication was
printed with permission of the authors and Cooperative Extension, an
educational agency of the University
of California and the
United States Department of Agriculture.